We plan to continue our detailed quantitative pathophysiologic and cytokinetic studies of RLV-type murine leukemia using standard hematologic and kinetic techniques. These studies will now be extended to include an evaluation of the potential therapeutic and prophylactic significance of erythropoietin and more conventional steroid drugs, and a study of developmental aspects of stem cell physiology in virally- infected mice subjected to agents which differentially stimulate blood cell formation, using standard stem cell assay procedures. Our hope is to develop a means to control virally-infected stem cell differentiation by experimental manipulation. In addition, we plan to examine the pathophysiology and cytokinetics of avian erythroblastosis and myeloblastosis with the aim of fully characterizing the fundamental defect responsible for these virally-induced dyscrasias in order to develop a sound therapeutic program.